improving the representation of estuarine processes in cesm · estuarine processes in cesm. sun,...

23rd Annual CESM Workshop, 2018National Center for Atmospheric Research

[email protected]

Improving the representation of estuarine processes in CESM

Qiang Sun①, Michael M. Whitney①, Frank O. Bryan②and Yu-heng Tseng③

① UCONN, Department of Marine Sciences② NCAR, Oceanography Section③ NTU, Institute of Oceanography


Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

CESM workshop - 2018 [email protected] Slide 2 of 14

Overview

Introduction

Development of Estuary Box Model (EBM) and results

Implementation of EBM in POP2 and results

Current work: Tracking riverine freshwater globally

Summary




The role of river in global hydrological cycle



[email protected] Slide 4 of 14

6

-6

1

-1

CESM workshop - 2018

Sea surface salinity bias: model (CESM) – climatology (WOA13)

Improving the representation ofestuarine processes in CESM



River runoff treatment in standard CESM• Applied as extra precipitation at sea surface.• Spreading around river mouth (300KM radius).• Discharge into ocean with ZERO salinity.• Using global reference salinity for VSF formula.

Improving river runoff by:• Remapping runoff as point source.• Introducing in the estuary mixing.• Local salinity for VSF formula.

(Tseng et al, Ocean Modelling, 2016)




Estuarine mixing in nature• Salty sea water

intrusions along bottom.

• Non-ZERO outflow at shallow depth.

• Mixing depends on both of runoff and tides.

http://www.ldeo.columbia.edu/~orton/salt_intrusion.html

Columbia River high discharge season

Columbia River low discharge season

River mouth

32PSU

5 PSU

32PSU

15 PSU



[email protected] Slide 7 of 14CESM workshop - 2018

Estuary Box Model (EBM): Two layer box

QR[QU]

H h

[SU]

[QL] SL

Landmodel

Ocean model

(Sun et al, Ocean Modelling, 2017)High Low

Salinity (Sun et al, Ocean Modelling, 2017)

Estuary Box Model (EBM): Control equationsContinuity:

Potential energy (PE) balance:

Salinity balance:




Estuary Box Model (EBM): Algebraic solutions

Estuary Box Model (EBM): Parameters and forcing2 Mixing parameters: ; 3 dimensional parameters:

with

3 Forcing terms: QR , Qt and SL




EBM outflow salinity vs. observations

EBM volume fluxes vs. ROMS

EBM compared with observations and ROMS in Columbia River

RMSE=1.7PSU, R2=70%

RMSE=513m3/s, R2=89%

(Sun et al, Ocean Modelling, 2017)




Estuary Box Model (EBM) global parameterization specification

Hudson

Chang Jiang

Chesapeake

Mississippi

STR

ATIF

ICAT

ION

RIVER DISCHARGE

*Geyer (2010)Sun et al, Ocean Modelling, 2017

Puget Sound

Estuary stratification-circulation diagram




Result (G-case): SSS difference with EBM – control casePSU

(Sun et al, Ocean Modelling, 2017)

31st to 60th year averaged sea surface salinity differenceimproved runoff – control run without improvement




Result (G-case): global assessment with salinity skill scores

Coastal ocean bands mask

Upper 150m ocean integrated salinity SS, with or without high latitude ocean.

Sun et al, JAMES, 2018 (in review)




Future work: global riverine freshwater pathway and influences




Summary The Estuary Box Model is a physically based parameterization of

unresolved estuarine mixing processes in the CESM.

The offline tests of EBM show very good agreement with direct observations of outflow salinity and high-resolution simulations of exchange flow volume fluxes.

A reduced set of parameters allows the parameterization to be practically applied to every river inflow point in global Earth system models at negligible cost.

The global CESM simulations with the EBM show it can have significant impacts on the salinity field of the coastal oceans, with non-negligible impacts in some open ocean areas.

The EBM can further imply in river borne nutrient and contaminants.



[email protected] workshop - 2018




Estuary Box Model (EBM): Implementation in POP2

with

and

Salt

Salt

Salt flux taken outof ocean: with local refence salinity

Salt flux taken fromdeeper to shallower:with local refence salinity

improving the representation of estuarine processes in cesm · estuarine processes in cesm. sun,...

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